Nuclear intermediate filament networks formed by A- and B-type lamins are major components of the nucleoskeleton. Lamins have growing links to human physiology and disease including Emery-Dreifuss muscular dystrophy (EDMD), lipodystrophy, cardiomyopathy, neuropathy, cerebellar disorders and segmental accelerated 'aging' syndromes. How lamins interact with other nucleoskeletal components, and even the identities of these other components, are open questions. Previous studies suggested lamins might bind actin. We report that the recombinant C-terminal tail domain of human A- and B-type lamins binds directly to purified actin in high-speed pelleting assays. This interaction maps to a conserved Actin Binding site (AB-1) comprising lamin A residues 461-536 in the Ig-fold domain, which are 54% identical in lamin B1. Two EDMD-causing missense mutations (R527P and L530P) in lamin A that are predicted to disrupt the Ig-fold, each reduced F-actin binding by ∼66%, whereas the surface-exposed lipodystrophy-causing R482Q mutation had no significant effect. The lamin A tail was unique among lamins in having a second actin-binding site (AB-2). This second site was mapped to lamin A tail residues 564-608, based on actin-binding results for the lamin C tail and internal deletions in the lamin A tail that cause Hutchinson-Gilford Progeria Syndrome (Δ35, Δ50) or restrictive dermopathy (Δ90). Supporting the presence of two actin-binding sites, recombinant precursor (unmodified) and mature lamin A tails (not C or B1 tails) each bundled F-actin in vitro: furthermore F-actin bundling was reduced 25-40% by the R527P, L530P, Δ35 and Δ50 mutations, and was abolished by Δ90. Unexpectedly, the mature lamin A tail bound F-actin significantly more efficiently than did the prelamin A tail; this suggested unmodified residues 647-664, unique to prelamin A, might auto-inhibit binding to actin (and potentially other partners). These biochemical results suggest direct mechanisms by which lamins, particularly lamin A, might impact the concentration of free actin in the nucleus or pathways including transcription, nuclear export, chromatin remodeling, chromatin movement and nuclear assembly that require nuclear myosin 1c and polymerizable actin.

中文翻译：

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肌动蛋白与 A 型和 B 型核纤层蛋白尾巴的直接结合和肌动蛋白丝束被 lamin A 尾的束缚

由 A 型和 B 型纤层蛋白形成的核中间丝网络是核骨架的主要组成部分。Lamins 与人类生理学和疾病的联系越来越密切，包括 Emery-Dreifuss 肌营养不良症 (EDMD)、脂肪营养不良、心肌病、神经病、小脑疾病和节段性加速“衰老”综合征。纤层蛋白如何与其他核骨架成分相互作用，甚至这些其他成分的身份，都是悬而未决的问题。以前的研究表明，核纤层蛋白可能与肌动蛋白结合。我们报告说，人 A 和 B 型核纤层蛋白的重组 C 末端尾域在高速造粒测定中直接与纯化的肌动蛋白结合。这种相互作用映射到保守的肌动蛋白结合位点 (AB-1)，该位点包含 Ig 折叠结构域中的 lamin A 残基 461-536，与 lamin B1 中的 54% 相同。核纤层蛋白 A 中两个导致 EDMD 的错义突变（R527P 和 L530P）预计会破坏 Ig 折叠，每个都将 F-肌动蛋白结合降低了约 66%，而导致表面暴露的脂肪营养不良的 R482Q 突变没有显着影响。纤层蛋白 A 尾部在纤层蛋白中是独一无二的，因为它具有第二个肌动蛋白结合位点 (AB-2)。根据 lamin C 尾部的肌动蛋白结合结果和 lamin A 尾部导致 Hutchinson-Gilford 早衰综合征（Δ35、Δ50）或限制性皮肤病（Δ90 ）。支持存在两个肌动蛋白结合位点，重组前体（未修饰的）和成熟的核纤层蛋白 A 尾（不是 C 或 B1 尾）每个都在体外捆绑 F-肌动蛋白：此外，R527P 将 F-肌动蛋白捆绑减少了 25-40%， L530P、Δ35 和 Δ50 突变，并被 Δ90 废除。出乎意料的是，成熟的核纤层蛋白 A 尾结合 F-肌动蛋白的效率明显高于前核纤层蛋白 A 尾；这表明未修饰的残基 647-664 是 prelamin A 独有的，可能会自动抑制与肌动蛋白（以及潜在的其他伙伴）的结合。这些生化结果表明，核纤层蛋白，尤其是核纤层蛋白 A，可能会影响细胞核中游离肌动蛋白浓度或途径，包括转录、核输出、染色质重塑、染色质运动和核组装，这些都需要核肌球蛋白 1c 和可聚合肌动蛋白。